The present invention relates to glass coated, separable impellers for use in closed, glass lined vessels to mix and agitate corrosive, adhesive, abrasive or easily contaminated ingredients such as acids, polymers, pharmaceuticals, dyes, food stuffs and the like.
Closed, glass lined vessels as used by the chemical, pharmaceutical or food industry may range in size to several thousand gallons and in the case of reactors, may be able to withstand relatively high internal pressures. In such vessels, it is desirable to have as small an access opening as possible to increase the integrity of the vessel and reduce the overall cost of vessel construction.
Since impellers used in these vessels may have an effective diameter or span equal to 40% to 60% of the vessel diameter the problem is how to provide such a vessel with an impeller of this size while limiting access openings to the size of manholes.
In the prior art this is accomplished by one of several means. For example, the impeller could have a split hub wherein the separate hub pieces, each with an impeller blade or two, could pass easily through a manhole size opening. The split hub would then be assembled to the end of the agitator drive shaft within the vessel by bolting or clamping the split hub pieces to the shaft. This is not entirely satisfactory because the fasteners used may loosen and those made of reactive metals to resist corrosion are frequently weak and always expensive. Also, protruding bolts or clamps provide places where product can accumulate as when mixing polymers.
Another way is to provide several hubs each with one or two impeller blades. These pass easily through a manhole opening and are stacked on the impeller drive shaft to provide a balanced three or four bladed impeller. This latter method is generally described in U.S. Pat. Nos. 2,811,339 and 3,494,708. While such construction has the advantage of the exposed surfaces being glass coated, the surface finishes and mechanical means needed to provide a gasketless, leak-proof connection are difficult to manufacture economically.
The present invention avoids the problems of split hubs or of the need to stack hubs by providing an impeller of unitary construction having four blades extending from a single hub in a unique, balanced arrangement which permits the impeller to pass through a manhole size opening even though the span of the unitary impeller is substantially greater than any manhole diameter.